End closure means for linear displacement potentiometers



July 9, 1968 F. F. GUGGENHEIM ETAL 3,392,360

END CLOSURE MEANS FOR LINEAR DISPLACEMENT POTENTIOMETERS Filed March 25, 1967 United States Patent O 3,392,360 END CLOSURE MEANS FOR LINEAR DISPLACEMENT POTENTIOMETERS Frederick F. Guggenheim, Teaneck, NJ., and Morris A.

Shriro, Mount Vernon, N.Y., assignors to Markite Corporation, New York, N.Y.

Filed Mar. Z3, 1967, Ser. No. 625,926 7 Claims. (Cl. 338-176) ABSTRACT OF THE DISCLOSURE An end closure arrangement for a potentiometer casing including an end plug biased by an internal spring into tight engagement with a resilient snap ring seated in a notch cut int-o the interior surface of the potentiometer casing. The end plug includes a shoulder portion which extends through the central aperture of the snap ring to prevent its radial collapse and thereby maintain the integrity of the ends of the potentiometer.

This invention relates to potentiomete-rs, and more particularly relates to linear displacement potentiometers which include novel end closure means for permanently lmaintaining the security of the ends thereof.

Broadly speaking, a linear displacemen-t potentiometer includes a hollow elongated housing within which is secured .at le-ast one relatively stationary resistance element. A shaft which is longitudinally displaceable relative to the axis of the housing extends both within and without the housing, with that portion of the shaft extending within thevhousing carrying contact means which are displaced relative to the stationary resistance element in response to the movement of the shaft by suitable .actuation of the external portion thereof. As well known in the art, movement of the contact means varies the potential appearing .at the output of the potentiometer.

Adequately and permanently closing the opposite ends of the housing of such linear potentiometers has presented problems which, up to the time of the instant invention, have not been satisfactorily overcome. Specifically, and as may be seen in United States Patent 2,790,052 issued to R. W. Armstrong on April 23, 1957, entitled Precision Resistance Device, prior art has suggested that the opposite ends of a linear potentiometer housing be closed by providing an elongated cylindrical member placed within the housing against the opposite ends of which are 4abutted suitably shaped plug members. The plug members are retained in position by suita-bly shaped resilient snap rings which are so dimensioned that a portion thereof ts within a groove provided in the interior surface -of the housing to prevent displacement relative thereto while at the same time a portion of such snapring is in blocking relationship with respect to the end plug to thereby prevent linear displacement of the end plug relative to the housing.

.It has been found, however, that with a closure system of the type shown in the aforementioned Armstrong patent, the resilient snap rings thereof have a -tendency to collapse radially when the potentiometer is exposed to vibration. That is, the snap ring tends to fall out, or actually fall inwardly, of the retaining groove provided on the interior surface of the potentiometer housing whereby the end plug, the cylindrical member, and in fact all internal parts of the potentiometer are free to slide longitudinally of the housing thereby destroying the precision required in such instruments, and eventually permitting complete disassembly thereof.

In contradistinction thereto, the instant invention provides an end closure means for a linear potentiometer 3,392,360 Patented July 9, 1968 which although generally similar to the above described prior art, prevents the corresponding snap rings from collapsing in the presence of vibration thereby permanently maintaining the security of the ends of the potentiometer. Thus precision is guaranteed over the extended life of the instrument while at the same time accidental disassembly is prevented.

Specifically, the instant invention includes at at least one end of the potentiometer an end plug which is urged outwardly by suitable biasing means provided on the interior of the potentiometer. Opposed to the outward movement of the biased end plug is a snap ring which is so dimensioned as to fit within a cutout notch or groove provided on the interior surface of the housing wall. As in the prior art, a portion of the snap ring extends in the linear path of movement of the end plug to prevent linear displacement thereof and thereby retain the assembled relationship of all internal parts of the potentiometer.

However, in the instant invention, where the plug is constantly biased into lirm engagement With its associated snap ring, and the snap ring is thereby firmly urged into frictional engagement with the opposing internal wall of the cutout notch which seats the ring, such snap ring iinds itself constrained in its blocking position and unable to collapse inwardly even in the presence of excessive vibration.

Furthermore, and in accordance with the instant invention, even the remotest possibility of the inward collapse of the snap ring is prevented by forming the outwardly disposed surface of the end plug with a shoulder portion in a manner to be further described, which fits within and under the snap ring whereby movement of such snap ring in the direction of collapse is positively prevented.

Accordingly, it is an object of the instant invention to provide end enclosure means for a linear displacement potentiometer which maintains the permanent security of at least one end of such potentiometer.

Another object of the instant invention is to provide such end closure means for a linear potentiometer which include at least one end plug urged outwardly by biasing means provided within the interior of the potentiometer and an appropriately secured snap ring which opposes the forces developed by such internal biasing means.

Still another object of the instant invention is to provide such end closure means wherein the above mentioned snap ring is tted within a recessed groove provided on the internal surface of the housing of the potentiometer such that frictional forces developed Iby the in-ternal biasing means oppose the direction of possible collapse of such snap ring to thereby maintain such snap ring in permanent lposition.

Another object of the instant invention is to provide such end closure means for a linear potentiometer wherein the end plug thereof is appropriately provided with a shoulder portion which iits within the above mentioned snap ring to prevent movement thereof in a direction which would cause collapse and ultimate disassembly of the potentiometer.

Still another object of the instant invention is to provide end closure means for a linear displacement potentiometer which maintain the permanent security of the opposite ends of such potentiometer.

Other objects and a fuller understanding of the instant i invention may be had by referring to the following dethe instant invention. Potentiometer includes an elongated hollow housing 12 which is preferably in the form of a hollow cylindrical shell. It is to be understood, however, that the housing 12 may be of rectangular crosssection, or for that matter of any other cross-section desired.

Broadly speaking, and as schematically shown in the drawing, the interior 14 of the housing 12 includes relatively stationary resistance means schematically shown at 16. Since the instant invention is directed to improvements in end closure apparatus, broadly designated 18 in the figure, a detailed explanation of the various types of internal resistance means such as 16 will not be presented, it being understood that a multitude of stationary resistance structures well known in the art may be utilized in a linear potentiometer incorporating the instant invention. For purposes of the instant invention it is sutiicient to note that with a given potential applied across the opposite end of the resistance 16, a predetermined portion of that potential may be produced as an output of the potentiometer in response to selective movement of a movable contact structure broadly designated 20 relative to the stationary resistance 16.

Although in no way limited to such disclosure, the movable contact means 20 may be secured to a block 21 suitably mounted on an internal portion 22 of a shaft 24 which has a portion thereof 26 extending out of the housing 12. The external portion 26 of the shaft 24 is preferably screw-threaded at 28, whereby the shaft 24 can be easily attached to a driver of some type to effect linear movement of the shaft 24 and contact means 20 relative to the stationary resistance means 16.

In accordance with the instant invention, there is provided end closure means designated at 18 for closing the opposite ends of the interior 14 of the housing 12. Such end closure means includes a pair of end plugs 30 and 32 which have an outer peripheral shape designated at 34 which corresponds to the inner surface designated 36 of the housing 12. Thus if the housing 12 were of circular cross-section so as to form a generally cylindrical shell, the plugs 30 and 32 would similarly be of circular cross-section, having an outer diameter slightly less than the inner diameter of the shell .12. If in fact the shell 12 were of different cross-section, then the plugs 30 and 32 would have a similar cross-section so as to mate with the interior of the housing. Plugs 30 and 32 include central passageways 38 and 40 through which shaft 24 may pass and plug 30 includes apertures 43 through which wiring may pass.

Provided within the interior 14 of the housing 12 and disposed about the shaft 24 is biasing means 42, preferably in the form of a single helical compression spring, the opposite ends of which abut the end plugs 30 and 32 to urge them in opposite directions.

To retain the end plugs 30 and 32 from axial movement which would otherwise be caused by the biasing means 42, there are provided generally resilient stop elements in the form of snap rings 44 and 46, the outer diameters of which are greater than the inner diameters of the housing 12 but less than the outer diameter thereof whereby such snap rings may iit within and be retained by aprpopriately shaped grooves or notches 48 and 50, respectively, in the housing wall 42.

It will be appreciated that axial forces developed by the compression spring 42 firmly urge the snap rings 44 and 46 against'the interior surfaces 54 and 56 of the notches 48 and 50, respectively, to generate high-frictional engagement between the snap rings and such surfaces to prevent such snap rings from collapsing radially inwardly when the potentiometer 10 is exposed to high or frequent vibratory shock. That is, with the snap ring firmly clamped by the biasing spring 42 between the end plugs 30 and 32 and the surfaces 54 and 56, respectively, such snap ring cannot easily slip out of its respective slots or notches 48 and 50.

Further, and in accord with the instant invention, to guarantee that the snap rings 44 and 46 may not collapse inwardly and thereby permit linear movement of the end plugs, even if the frictional forces developed between the snap rings and their respective coacting surfaces 54 and S6 do not retain the snap ring in position, the end plugs 30 and 32 are provided with notched shoulder portions 58 and 60, the outer diameters of which correspond to the inner diameter of the snap rings. Thus with the snap rings 44 and 46 in their installed condition, it is physically impossible for the snap ring to be displaced radially inward toward the shaft 24 and the integrity of the ends of the potentiometer is assured.

It will be appreciated that the biasing means 42, while constantly generating high frictional engagement between the snap rings and the surfaces 54, 56 of the notches 48, 50, respectively, simultaneously and necessarily continually bias the end plugs 30, 32 such that the shoulder portions 58, 60 thereof will remain in their seated positions within the internal diameters of the snap rings.

ln assembling the potentiometer 10 of the instant invention all internal elements are iirst inserted within the casing 12 and as the last step, the end plugs 30, 32 are urged inwardly toward one another against the bias of compression spring 42 such that the snap rings 44, 46 may be inserted into their cooperating slots 48, 50. Finally, the end plugs are allowed to separate (under the influence of the biasing spring 42) whereby the shoulder portions 5S, 60 thereof will pass through the associated snap rings to complete the assembly.

It is to =be understood that although two identical end elements or plugs have been shown, obviously one could practice the instant invention in an environment where there might be a closed or sealed end at one of the potentiometer and therefore only one end element or plug need be provided and retained in place in accordance with the instant invention. Similarly, it is to be understood that event where -tw-o end elements or plugs are being utilized, it is not necessary that they be of identical configuration as shown in the drawings.

It may be noted that because of the permanent end closure 'achieved with the instant invention, the plugs 30 and 32 may lbe utilized as mounting points to secure the potentiometer 10 to -any external surface. Thus in the ligure, the plugs 30 and 32 are provided with internally bored passageways `62 and 64 into which may be threaded suitable fastening means for mounting the potentiometer 10 to any external surface desired. This is to be contrasted with the prior art wherein because the end sections of potentiometers are subject to displacement and possi-ble disassembly in the presence of shock environment, it was required to -utilize mounting means in the form of retaining rings of some type surrounding the external surface of the housing 12 to which are attached suitable feet. It is to be also appreciated that because of the tight, continually biased, frictional engagement between the plugs and their associated snap rings, the instant invention has excellent sealing characteristics.

Thus there has been described a novel combination of elements which are so arranged as to permanently maintain the integrity of the opposite ends of an elongated potentiometer housing even in the presence of high shock environments.

Although there has been described a preferred embodiment of this novel invention, many variations and moditications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, lbut only by the appending claims.

What is claimed is:

`1. In a potentiometer which includes a hollow housing; a shaft longitudinally displaceable relative to the axis of said housing, said shaft including a first portion disposed without said housing and a second portion disposed within said housing; and cooperating resistance means and contact means, the positions of which relative to each other may be changed by longitudinal displ-acement of said shaft; the improvement comprising end closure means comprising:y

an end element having a cross-sectional shape corresponding to the cross-sectional shape of said housing, said end element being located within said housing at said first end thereof;

biasing means disposed Within said housing for urging said end element in an outward direction relative to the inte-rior of said housing; and

stop means positioned within said housing for preventing linear movement of said end element in said outward direction; said stop means including a first portion in blocking relationship with respect to said end element, and a second portion maintained restrained from movement by an internal portion of said housing.

2. In a potentiometer which includes a hollow housing; a shaft longitudinally displaceable relative to the axis of said housing, said shaft including a first portion disposed without said housing and a second .portion disposed within said housing; and cooperating resistance means and contact means, the positions of which relative to each other may -be changed by longitudinal displacement of said shaft, the improvement comprising end closure means comprising:

an end element having a cross-sectional shape corresponding to the cross-sectional shape of said housing, said end element being located within said housing at said first end thereof; biasing means disposed within said housing for urging said end element in an outward direction relative to the interior of said housing; and

stop means associated with said end element and retained motionless relative to said housing for preventing linear movement of said end element in said outward direction;

wherein said stop means includes a ring-like member having an outer dimension greater than the interior dimension of said housing land less than the outer dimension of said housing, and said housing includes a groove on the interior surface thereof within which said ring-like member is retained, said ring-like mem-ber having a portion which is in blocking relationship with respect to said end element to prevent linear movement of said end element in said outward direction.

3. Apparatus of claim 2 wherein said groove includes an interior surface against which said ring-like member is firmly pressed by said end element as a result of the .force developed by said biasing means, whereby frictonal forces developed between said ring-like member and said interior surface of said groove prevent said ring-like member from being displaced axially of said housing.

`4. Apparatus of claim 3 wherein said ring-like member has a predetermined inner ydimension to define a passageway therethrough, and said end element includes a shoulder portion which passes through said passageway to prevent axial movement thereof.

5. In a potentiometer Iwhich includes a hollow housing; a sha-ft longitudinally displa-ceable relative to the axis of said housing, said shaft including a first portion disposed without said housing and a second portion disposed within said housing; and cooperating resistance means and contact means, the positions of which -relative to each other may be changed by longitudinal displacement of said shaft, the improvement comprising end closure means comprising:

lan end element having a cross-sectional shape corresponding to the cross-sectional shape of said housing, said end element being located within said housing at said first end thereof;

biasing means disposed within said housing for urging said end element in an outward direction relative to the interior of said housing; and

stop means associated with said end element and retained motionless relative to said housing for preventing linear movement of said end element in said outward direction; and

further in-cluding second end closure means for closing a second end of said housing opposite said first end, said second end closure means comprising:

a second end element having a cross-sectional shape corresponding to the cross-sectional shape of said housing, said second end element being located within said housing at said second end `thereof and being urged by said biasing means in a second outward direction opposite the outward direction said first end element is urged; and

second stop means associated with said second end element and retained motionless relative to said housing for preventing linear movement of said second end element in said second outward direction.

6. Apparatus of claim 5, wherein said second stop means comprises a ring-like member having an outer dimension greater than the interior dimension 0f said housing and less than the outer dimension of said housing, and said housing includes a second groove on the interior surface thereof within which the ring-like member of said second stop means is retained, said ring-like member of said second stop means `having a portion which is in blocking relationship with respect to said second end element to prevent linear movement of said second end element in said second outward direction.

7. Apparatus of claim 6 wherein said ring-like member of said second stop ymeans has a predetermined inner dimension to define a passageway therethrough, and said second end element includes a shoulder portion which passes through said passageway of said ring-like member of said second stop means to prevent axial movement thereof.

References Cited UNITED STATES PATENTS 2,669,876 2/1954 lLentz 338-178 X ROBERT K. SCHAEFER, Primary Examiner.

H. I. HOHAUSER, Assistant Examiner. 

